1. Field of the Invention
The present invention relates generally to suspension systems for hard disk drive systems. More specifically, the invention relates to lifters used in hard disk drive suspension assemblies. Most specifically, the invention relates to lifters designed to cope with high shock conditions.
2. Related Art
Disk drive head suspensions, or head gimbal assemblies, are well known in the art. These assemblies typically comprise a load beam and a flexure, the load beam extending longitudinally from a base plate, and the flexure moveably coupled to the load beam. A dimple displaced between the flexure and load beam provides a pivot point for the flexure. A read/write head, typically mounted at or near the distal end of the flexure, reads data from and writes data onto a disk surface during high-speed rotation of the disk within influential range of the head. Movement of the disk past the head creates aerodynamic flow exploited by the head to create an air bearing which maintains a minute separation form the head to the disk. The load beam is pre-loaded such that, during steady-state conditions, the pre-load force counteracts the lift force to advantageously suspend the read/write head at an optimal distance from the disk surface. In an unloaded condition, the load beam maintains a minimum lift clearance from the disk surface. Normally, the lift clearance between load beam and disk surface is in the range of 0.35 mm to 0.75 mm.
During a shock event, vertical movement of the suspension assembly may occur, causing the read/write head to impact the disk surface. This action may cause damage to the read/write head, load beam, or flexure, and permanently alter the lift clearance. In severe cases, the impact may damage the disk surface, causing loss of stored data. Shock conditions may result from normal operation, for example, during loading or unloading of a disk. Other sources of shock include non-operational phenomena such as shipping, handling, or installation that cause external jarring or impact to the system. Disk drive systems used in mobile applications are especially subject to shock.
A desired shock rating for disk drive systems typically ranges between 500 g/gm and 1000 g/gm. To meet this criteria, lifters are designed for high stiffness and low mass in order to optimize shock performance. Generally, a high stiffness dampens suspension system response to shock, and provides a lifter with sufficient material strength to resist deformation and withstand shear forces. In addition, a low mass minimizes the reactive forces transmitted by the lifter to interconnected suspension assembly components. However, a tradeoff occurs when attempting to achieve these design objectives. Greater stiffness is achieved at the expense of higher mass, and reducing mass tends to lower stiffness. A lifter stiffness of at least 800 N/m may be required for certain applications. Meeting this criteria while maintaining the shock rating is especially challenging for designers.
The effectiveness of a forming technique used to form shock-resistent limiters varies according to the thickness of the base material. Previous techniques used on thick material cannot be applied effectively to thinner materials that are required for low mass/high shock applications. One such technique, typically employed on thicker materials, is known as M-forming. M-forming consists of configuring a lifter with an M-shaped cross section 101, as shown in FIG. 1. M-forming is attractive from a manufacturing standpoint because the forms are cylindrical in character, and relatively easier to fabricate than conical shapes in hard material. However, one drawback of applying M-forming on thin material is difficulty in achieving high stiffness—an M-formed stiffness on the order of 500 N/m is typical. Another drawback of M-forming is that it limits the amount of offset that can be achieved between the bottom of the lifter and lowest point on the load beam. In order to form a higher offset, a wider load beam may be used, but that adds more mass to the lifter thereby reducing shock performance. Another technique used for thick base materials is known as jog-forming, which consists of adding an upward-sloping ramp, or jog 201, between the load beam and lifter, as shown in FIG. 2. Although jog-forming allows for a higher offset, stiffness and shock performance tend to be lower than an M-formed lifter. Thus, both of these techniques produce lifters having a stiffness/mass tradeoff that is too limiting to meet the most demanding shock performance ratings.
In view of the foregoing, there is an ongoing need to improve the shock performance of limiters in disk drive suspension systems.